The present invention relates to a cutting tool and, more particularly, to a damper for a cutting tool.
During an operation of cutting a work piece with a cutting tool, vibration inevitably occurs and affects the precision of the operation. It is therefore a practice to reduce the vibration by inserting a damper within a shank of the cutting tool.
Dampers have been disclosed in documents such as Japanese Patent Application Publication Nos. 2001-96403, 2003-62703, 2003-136301, 2005-177973, 1994-31505 and 1994-31507 and Japanese Patent Publication No. 2979823.
Japanese Patent Application Publication No. 2003-136301 discloses a cutting tool including a blade attached to a front end of a shank. A deep hole is defined in the shank. The deep hole includes an open end at a rear end of the shank and a closed end near the front end of the deep hole. A damper is inserted in the deep hole, adjacent to the blade. A super hard core is inserted in the deep hole, behind the camper.
Japanese Patent Application Publication No. 1994-31507 discloses a cutting tool including a shank. Viscous fluid and a balancing block are introduced into a deep hole defined in the shank.
Japanese Patent Publication No. 2979823 discloses a helical spring inserted in a deep hole defined in a shank of a cutting tool and a viscous elastic material provided between the helical spring and a closed end of the deep hole. A blade is attached to the helical spring. A frictional, vibration-absorbing material is provided between the blade and the shank for transforming vibration into heat that can be dissipated, thus reducing the vibration.
In each of the foregoing references, it is difficult to make the deep hole in the shank where the external diameter of the shank is small. It requires a deep-hole drill to make the deep hole in the shank, and this is expensive. Moreover, the deep hole compromises the strength of the shank. Moreover, the structure is complicated and entails a high cost.
Japanese Patent Application Publication No. 1994-31505 discloses a shank including a bore defined therein for receiving a damper made of a different material. Friction between the shank and the damper reduces the vibration.
Japanese Patent Application Publication Nos. 2001-96403 and 2003-62703 both disclose a damping material introduced into a bore defined in a shank of a cutting tool. The damping material absorbs the energy of the vibration, thus reducing the vibration. In addition to the foregoing problems, these references involve the use of the damping material including Mn—Cu alloys that are often expensive and cannot be fabricated easily. Therefore, it is difficult to reach a high performance at a low cost according to these references.
Japanese Patent Application Publication No. 2005-177973 is intended to provide a cutting tool with excellent damping at a low cost by making a polygonal pocket in a shank of a cutting tool, inserting a damper in the pocket and closing the pocket with a cover, thus keeping the damper in the pocket. The damper can be strip-like, cylindrical or polygonal. The damper is not connected to the shank, with a gap between them. During an operation of cutting a work piece with the cutting tool, the damper alternatively hits different portions of the wall of the pocket because of inertia, thus reducing vibration. The effect of the reduction of the vibration depends upon the gap. The effect of the reduction of the vibration is poor if the gap is too small or too big. It is however difficult to keep the gap within an appropriate range.
Thus, there is a need for an inexpensive and effective damper for a cutting tool.